The increasing performance requirements for semiconductor devices have led to the development of new materials which will improve the electrical performance of the devices. In recent years, much of the materials development has centered on electrically conductive materials which can be deposited as a thin film, are oxidation resistant, and provide a barrier to the diffusion of elements through the material. In general, conductive metal oxides meet many of these requirements. Conductive metal oxides include oxides of selected Group VIII metals. One metal oxide which has received considerable attention is ruthenium oxide. Ruthenium oxide possesses many desirable properties such as high electrical conductivity, chemical stability, and oxidation resistance.
While the identification of materials have desirable properties is an important first step, the new material cannot be used in a semiconductor device unless process technology exists to deposit the material and to pattern the material into the necessary geometric structures required for component fabrication. Thus, the introduction of new materials often requires new process technology to fabricate semiconductor devices incorporating the new material.
In the case of ruthenium oxide, suitable deposition techniques exist; however, etching the ruthenium oxide once deposited has proven difficult. For a new material to have any utility in a semiconductor device, the material must be capable of being patterned by a high resolution photolithographic and etching process. However, ruthenium oxide is an especially resilient material which is not soluble in many common liquid etchants. Additionally, attempts at dry etching have been generally unsatisfactory. However, some success has been attained by the dry etching of ruthenium oxide using fluorinated carbon compounds. In addition, sputter etching using noble gases such as argon removes ruthenium oxide, but at a low etch rate.
An important characteristic of an etch process to be used for advanced semiconductor devices is that the etch preferentially removes ruthenium oxide without etching an underlying dielectric material. While plasma etching with a fluorinated gas or argon gas provides a dry etching technique, fluorinated carbon compounds, such as carbon tetrafluoride, are known to also rapidly etch many dielectric materials, such as silicon oxide, silicon nitride, and the like. Additionally, plasma etching with carbon tetrafluoride is known to have a high lateral etch rate under almost all RF power and vacuum pressure conditions. Lateral etching is undesirable because it undermines the edges of the patterning material used to define features on the substrate surface. Furthermore, sputter etching is non-selective to underlying materials because of the high ion energy created by the sputter etching apparatus. Therefore, a suitable etching process must be capable of high etch selectivity to underlying layers and provide high resolution pattern transfer.